(1) Field of the Invention
The present invention relates to a method of manufacturing an electric double-layer capacitor that is used for regeneration or power storage of various electronic devices and hybrid vehicles.
(2) Description of Related Art
FIG. 9 is a sectional view of a conventional electric double-layer capacitor 501 disclosed in patent document 1. Hollow portion 10A is provided in capacitor element 10. A polarizable electrode layer is formed on each of two collectors made of aluminum foil having a strip shape. Positive electrode 15A is disposed on one end side in the width direction of one collector. Negative electrode 15B is disposed at an end of the other collector in the opposite direction to positive electrode 15A. A separator is provided between the collectors. The collectors and the separator are wound around hollow portion 10A, providing capacitor element 10. Electrodes 15A and 15B are exposed at end surfaces of capacitor element 10 opposite to each other.
Cylindrical case 11 having a bottom, made of metal, such as aluminum, accommodates capacitor element 10 and a driving electrolyte. Negative electrode terminal 11A for external connection is provided unitarily on an outer bottom surface of case 11. Projection 11B is provided unitarily on an inner bottom surface of case 11, and is inserted into hollow portion 10A of capacitor element 10. Negative electrode 15B of capacitor element 10 accommodated in the case 11 is joined mechanically and electrically to the inner bottom surface of case 11 by laser welding.
Positive electrode terminal 12A for external connection is provided unitarily on an outer surface of sealing plate 12 made of aluminum. Projection 12B is inserted into hollow portion 10A of capacitor element 10. The driving electrolyte is put into case 11 through injection port 12C. Pressure regulating valve 13 regulates the pressure in case 11. Positive electrode 15A of capacitor element 10 is joined mechanically and electrically to an inner surface of sealing plate 12 by, for example, laser welding. An opening edge of case 11 is wound with a periphery of sealing plate 12, thereby being sealed with sealing plate 12, which is called a curling process.
In electric double-layer capacitor 501, electrodes 15A and 15B provided on both end surfaces of capacitor element 10 are joined directly to case 11 and sealing plate 12 with small connection resistances, respectively.
FIG. 10 is an enlarged sectional view of capacitor element 10. Electrodes 15A and 15B exposed at both end surfaces of capacitor element 10 are provided at low density because only respective ones of the electrodes are exposed at respective ones of both end surfaces. The low density prevents electrodes 15A and 15B from being pressed stably on and being welded to case 11 and sealing plate 12.
This welding is performed by radiating a laser beam from the outer bottom surface of case 11 and the outer surface of sealing plate 12 while the inner bottom surface of case 11 and the inner surface of sealing plate 12 are pressed on electrodes 15A and 15B. This operation prevents electrodes 15A and 15B from melting enough to be welded.
In order to weld case 11 and sealing plate 12 to electrodes 15A and 15B reliably, projections are provided on the inner bottom surface of case 11 and the inner surface of sealing plate 12. Electrodes 15A and 15B are welded with a laser by pressing the projections onto electrodes 15A and 15B. However, only portions of the electrodes on which the projections are pressed may be welded reliably, but other portions cannot be welded stably.
In electric double-layer capacitor 501, electrodes 15A and 15B are welded to the inner bottom surface of case 11 and the inner surface of sealing plate 12 with the laser, thereby joining capacitor element 10 mechanically and electrically to case 11 and sealing plate 12. Upon being used for vehicles, electric double-layer capacitor 501 is required to withstand large vibrations.
In electric double-layer capacitor 501, a gap is provided between an outer circumferential surface of capacitor element 10 and an inner surface of case 11. When large vibration is applied to electric double-layer capacitor 501, capacitor element 10 moves in case 11. This applies a stress to joined portions between electrodes 15A and 15B and case 11 and sealing plate 12, which can cause the joined portions to break.    Patent document 1: Japanese Patent Laid-Open Publication No. 2004-134632